Wednesday November 5 2014
Back pain is a leading cause of disability
"Smokers are three times more likely to suffer from back pain," the Mail Online reports. The headline was prompted by the results of a recent study, which involved observing 68 people with sub-acute back pain (back pain lasting for 4 to 12 weeks with no back pain in the previous year) over one year.
The participants completed repeated questionnaires about their level of back pain and had four functional MRI brain scans over the course of the year.
Smokers were three times more likely to develop chronic back pain. They were also more likely to have increased activity in the brain pathways implicated in addiction (between the nucleus accumbens and the medial prefrontal cortex).
The researchers speculate this increased activity may also increase the risk of chronic pain developing. This increase in activity reduced in a small number of people who stopped smoking.
As this was an observational study, it cannot prove that the increased brain pathway activity or smoking caused the back pain to become chronic, but it does indicate they may be linked in some way.
Even if you don't suffer from back pain, there's no excuse not to try to quit smoking. It can cause lung cancer and heart disease, and increase your risk of a stroke – all of which can be fatal.
Where did the story come from?
The study was carried out by researchers from the Feinberg School of Medicine in the US, and was funded by the US National Institutes of Health.
It was published in the peer-reviewed medical journal, Human Brain Mapping.
The study was generally reported accurately by the Mail Online, although it didn't emphasise that the findings were only based on 68 people.
Similarly, the study was about how smoking influenced the risk of people moving from experiencing sub-acute back pain to chronic back pain, but this subtlety seemed to be lost.
Based on the headlines, readers may get the wrong impression that the study was about developing back pain full stop.
Also, the Mail's claim that "quitting can ease symptoms" – while well meaning – is unsupported by the evidence of this study.
What kind of research was this?
This was a longitudinal study looking at the potential relationship between developing chronic back pain and smoking tobacco.
Previous research suggested the brain pathways involved in addiction are also related to those implicated in the development of chronic pain.
The researchers aimed to test the theory people with new-onset back pain would be more likely to develop chronic back pain if they were smokers.
As this was a type of observational study, it cannot prove smoking causes a transition to chronic back pain, but it can show potential links that can be tested in more rigorous studies in the future.
It is often difficult to tease out the precise relationship between smoking and chronic back pain. Smokers tend to be unhealthy in other ways, such as not taking very much exercise, so this could also have a confounding effect.
What did the research involve?
The year-long study involved participants completing well-validated questionnaires about:
- pain (McGill short form)
- depression (Beck's Depression Inventory)
- positive or negative feelings and emotions (Positive Affective Negative Affect Score, PANAS)
- demographic information, including smoking status
After an initial visit, participants were assessed on four more occasions during the year using further questionnaires. They also had their brains scanned using functional MRI scans, which can – at least to a certain extent – measure brain activity.
Three groups of people were included in the research. The first and largest group consisted of 160 people with sub-acute back pain, defined as back pain lasting for 4 to 12 weeks with no back pain in the previous year. Of these, 123 were recruited to the study and 68 people completed follow-up after one year.
The second group included 32 people with chronic back pain for more than five years, of whom 24 completed the study. The third group of 33 people was considered to be the control group. These people had no back pain, and 19 completed the study.
For all groups, the researchers analysed whether smoking was linked to their back pain.
What were the basic results?
Of the 68 people with sub-acute back pain, 31 were considered to be recovering according to a pain decrease of at least 20% after one year (six of these were smokers and 25 were non-smokers). The other 37 had persistent pain (16 smokers and 21 non-smokers).
Those with persistent pain were three times more likely to be smokers than those who recovered, (odds ratio [OR] 3.17, 95% confidence interval [CI] 1.05 to 9.57) despite having similar levels of initial back pain.
They were also more likely to have increased activity in the brain pathways implicated in addiction (between the nucleus accumbens and the medial prefrontal cortex).
In nine participants with sub-acute back pain or chronic back pain, this brain pathway activity reduced after they quit smoking, but it is unclear what effect this had on their back pain.
Smoking also did not appear to relieve pain, as smokers did not have reduced back pain intensity either at baseline or after one year compared with non-smokers, and back pain did not increase when people stopped smoking.
At baseline, people with sub-acute back pain and chronic back pain were more likely to be smokers than controls. And the pain was also likely to have a negative impact on their mood, according to higher scores on the Beck Depression Inventory and negative PANAS scores.
How did the researchers interpret the results?
The researchers concluded that, "Smoking increases risk of transitioning to CBP [chronic back pain], an effect mediated by corticostriatal circuitry involved in addictive behaviour and motivated learning."
This longitudinal study found sub-acute back pain was three times more likely to progress to persistent back pain in smokers.
The researchers presented functional MRI findings, which indicated brain pathways that could be involved in this process. But further research will be required to fully understand the mechanisms at play.
The study did not find that smoking provided any pain relief, and indeed the pain intensity did not increase for those people who stopped smoking.
The study sample was quite small, meaning the results may not be applicable to larger and more diverse groups of people. As such, the results are not conclusive and should not be taken at face value.
The general advice for the early management of lower back pain is:
- to continue normal activities as far as possible
- to stay physically active and exercise within your capabilities
- if medication is required, start with paracetamol and then consider other options, such as non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen, with appropriate stomach protection
While this research is not conclusive, there are many health benefits associated with stopping smoking that have a large and robust evidence base, such as a reduced risk of lung cancer and heart disease.
Read more advice about effective methods known to help many smokers quit.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.